The Evolution of Massive Stars After Hydrogen Exhaustion in the Core.

Abstract

view Abstract Citations (1) References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Evolution of Massive Stars After Hydrogen Exhaustion in the Core. Hayashi, Chushiro ; Cameron, Robert C. Abstract Computations of advanced evolutionary phases were made for a Population I star of 15.6 solar masses, whose hydrogen-burning phase was treated by S. Sakashita, Y. Ono, and C. Hayashi 1959, Prog. Theoret. Phys. (Kyoto) 22, 531]. The effect of radiation pressure was taken into account. The helium-burning phase accounts for the early-type supergiant branch of the H-R diagram of the double cluster h and N Persei. A gravitational contraction phase begins during hydrogen burning when Xeore=0.005. The effective temperature increases slightly for 1.4 X 10~ years until Xc0re=0.00003. The envelope then expands, while the inner regions continue to contract until gravitation is providing most of the star's energy. At Te <90000K, the direction of evolution in the H-R diagram again reverses and the star begins to burn helium as an A-type star near the low-temperature end of the early-type supergiant branch of h and N Persei. For this phase we essentially repeated the work of C. Hayashi, J. Jugaku, and M. Nishida [1959, Prog. Theoret. Phys. (Kyoto) 21, 315], but included the effect of the conversion of helium to carbon on the mean molecular weight. We find higher central temperatures for the later stages of helium burning and also a reversal of direction of the evolutionary track when the star has become a late B-type with Ycore=0.35, after 8.2x 10~ years of helium burning. The star reaches the M-type super- giant region in an additional 3.4 x 1 0~ years with Ycore=0.01S and a central temperature of 3.2x 108 0K. The mass of the convective core during helium burning increases monotonically. Thus the dependence of the later evolutionary phases on the star's helium- burning history is small. Preliminary results have been obtained for the subsequent carbon (or neon) burning phase, indicating a very large stellar radius, which will be reduced considerably when the outer convective zone is taken into account. This phase will probably account for the M-type supergiant branch of h and N Persei. The central temperature at the onset of carbon burning is 7 X 108 0K and the central density is 40000 g/cm2. Publication: The Astronomical Journal Pub Date: 1960 DOI: 10.1086/108170 Bibcode: 1960AJ.....65T.490H full text sources ADS |